It is known that an endoscopic treatment instrument is inserted into a channel of an endoscope inserted into a body such that various treatments are performed on a target portion within the body by a treatment portion formed on a distal end of the endoscopic treatment instrument which projects from a distal end of an inserted portion of the endoscope. It is known that the treatment portion is formed in various shapes depending on treatments performed on a target portion. For example, there are provided a loop-shaped high-frequency snare, which is used when a root such as a polyp or the like is tightened and excised, and a hook-shaped knife which is used when a mucosa or the like is excised. In this case, the treatment portion needs to be rotated around an axis of the channel so as to face an appropriate direction with respect to the target portion, or the treatment portion facing an appropriate direction needs to be restricted from being rotated. Accordingly, a method is proposed, in which a side portion of a treatment portion passing through the inside of the channel is fitted into a fitting groove, which is formed in the vicinity of a distal end of a channel and becomes thin toward the distal end, such that the rotation of the treatment portion is restricted (for example, refer to Patent Document 1). Further, a method is proposed in which a direction control member provided in the rear side of a treatment portion of an endoscopic treatment instrument is fitted into a fitting groove within a channel so as to restrict rotation (for example, refer to Patent Document 2). In addition, a method is proposed, in which an endoscopic attachment is mounted on a distal end of an inserted portion of an endoscope, a hood opening portion of the endoscopic attachment is formed in a shape corresponding to the shape of the treatment portion, and the rotation of a treatment portion is restricted by the hood opening portion when the treatment portion passes through the endoscopic attachment (for example, refer to Patent Documents 3 and 4).
However, in the method where the fitting groove is provided inside the channel of the endoscope, the treatment portion or the projecting direction control member corresponding to the fitting groove is inserted into the channel. Therefore, the inner surface of the channel may be damaged. Further, when the rotation is restricted by the direction control member, the opening of the channel is reduced in size at the distal end where the fitting groove is formed, by the area occupied by the fitting groove. Therefore, when a treatment instrument having no direction control member is used in the endoscope, only an endoscopic treatment instrument corresponding to the shape of the distal end can be used. Further, in the method where the direction is restricted by the fitting groove within the channel corresponding to the shape of the treatment portion or by the endoscopic attachment on the distal end of the inserted portion, if the treatment portion passes through the corresponding restricting portion so as to project from the distal end of the inserted portion, the restriction is released.
Patent Document 1: Japanese Patent No. 3482022
Patent Document 2: JP-A-H8-168492
Patent Document 3: JP-A-2002-112946
Patent Document 4: JP-A-2000-354581